As expectations for ever-more capable electronic devices continues to grow, devices such as personal computers are expected to provide increasingly fast processing to deliver applications such as streaming video, rapid Internet surfing, and realistic computer gaming. One strategy to provide fast processing is to design circuitry to operate at higher clock frequencies, since other things being equal, operating circuitry at higher clock frequencies allows the circuitry to perform a given function in a shorter amount of time. For example, whereas in 1995 a Pentium chip from Intel Corp. could be operated with a 100 MHz (100 million cycles/second) clock rate, by 2002 an Intel Pentium 4 could be operated with a clock rate of 3 GHz (three billion cycles/second).
Such high clock rates can lead to a number of design issues. For example, one issue that can cause problems is jitter. Jitter is an abrupt and unwanted variation in a signal, such as a variance in the interval between successive cycles of the clock, known as period jitter.
Another issue is clock skew, in which a clock signal arrives at various points of consumption (components using the clock signal to provide a function) at different times. Typically, clock skew can result from manufacturing “process corner” variations across a number of circuits on a die, or voltage and/or temperature variations during operation, and the like. In addition, clock skew can be affected by the distance that the clock signal travels from the point of generation to the various points of consumption, such that a longer distance may more likely cause the clock signal to arrive at the various points of consumption at different times.